1. Field of the Invention
This invention generally relates to a system and method for monitoring intravascular infusion of parenteral fluid from a parenteral fluid delivery system to a patient, and more particularly relates to numerical, objective evaluation of effectiveness of intravascular fluid delivery, by monitoring fluid flow parameters of resistance and compliance.
2. Description of Related Art
Systems for infusing parenteral fluids intravenously to a patient by means of an infusion pump typically include a bottle of parenteral fluid, and an intravenous (IV) set which includes a drip chamber, flexible plastic tubing extending from the drip chamber, and a cannula at the end of the tubing to be inserted into a patient's blood vessel for delivery of the parenteral fluid. An infusion pump, such as a peristaltic pump, is typically used for driving the parenteral fluid through the tubing at a desired rate. Common problems in such a system are that the fluid flow may become occluded, that the needle inserted into a patient's vein may be dislodged, or that the discharge tip of the needle becomes partially dislocated so as to deliver fluid in adjacent interstitial tissue, which may cause serious injury.
Systems have been devised for the detection of abnormalities in an intravascular infusion system, by use of simple monitoring of the infusion pressure. A high or increasing pressure may be interpreted as either an infiltration or an occlusion. A low pressure may be interpreted as as an unobstructed line. However, the pressure required to achieve a given flow in an intravascular system depends on many factors, such as motion and position of the patient, respiration and arterial or venous blood pressure of the patient, and the size and position of the cannula used. Such factors create a considerable uncertainty in the measurement of pressure, and may cause difficulty in interpretation of pressure readings. Observation of a pressure response of the fluid delivery system, to determine whether pressure returns to a normal steady state equilibrium within a given time period can give some information as to effectiveness of fluid delivery. Application of fluid flow excitation pulses and comparison of pressure responses of the system against a reference value is also known.
It would be desirable to provide a system for monitoring fluid in an intravascular parenteral fluid delivery system which provides a measure of resistance to fluid flow and a measure of compliance of the patient's tissue. Resistance to flow is appropriate for monitoring flow to an infusion site, since it can indicate such problems as having the end of the cannula pressed against the vein or artery wall, the cannula being infiltrated into the tissues surrounding the vessel, and certain medical problems such as phlebitis which involve constriction of the vessel. Compliance may be used for distinguishing the location of the cannula due to a significant difference between the compliance of a vein and the compliance in interstitial tissue.